RestSharp ExecuteAsync UI not waiting for rest call completion - asp.net-web-api

Question

I have been trying to use download a file from my angular 6 application by calling an API method GetFile() written using NancyFx.
The GetFile() API method again calls a web API method GetRemoteFile() using RestSharp.
The GetFile() method follows the async/await pattern. But I see that the file gets downloaded before the success callback of GetRemoteFile() is even being called.
And because of this the downloaded file is 0 bytes.
using RestSharp.Extensions.MonoHttp;
using System;
using System.Collections.Generic;
using System.IO;
using System.Net.Http;
using System.Threading.Tasks;
using System.Linq;
using Nancy.Json;
using RestSharp.Extensions;
using System.Net;
using Nancy;
using Nancy.Responses;
using RestSharp;
private async Task<Nancy.Response> GetFile(int orderId)
{
var request = new RestRequest($"api/GetRemoteFile", Method.POST);
string json = SomeBodyData();
request.AddJsonBody(new RemoteParameter
{
OId = documentId,
Json = json
});
var taskCompletionSource = new TaskCompletionSource<IResponse>();
client.BaseUrl = new Uri("http://someremoteapi.com/orders/");
var res = client.PostAsync(request, (response,handle) =>
{
taskCompletionSource.SetResult(response);
});
var data = await taskCompletionSource.Task;
var stream = new MemoryStream(data.RawBytes);
stream.Position = 0;
var file= new StreamResponse(() => stream, "text/csv");
return file;
}

Answer 1

Follow the async flow and await ExecuteTaskAsync. With that, you should be able get the desired behavior.
private async Task<Nancy.Response> GetFile(int orderId) {
var request = new RestRequest($"api/GetRemoteFile", Method.POST);
string json = SomeBodyData();
request.AddJsonBody(new RemoteParameter {
OId = documentId,
Json = json
});
client.BaseUrl = new Uri("http://someremoteapi.com/orders/");
var response = await client.ExecuteTaskAsync(request);
var stream = new MemoryStream(response.RawBytes);
stream.Position = 0;
var file= new StreamResponse(() => stream, "text/csv");
return file;
}